This invention relates to an improved exhaust gas oxygen sensor of the type adapted for installation in a conduit for conveying exhaust gases from an internal combustion engine. The improved sensor is responsive to the partial pressure of oxygen in the exhaust gases to which the sensor is exposed and has an electrical characteristic which varies, when the sensor is at operating temperatures in the range from about 350.degree. C. to about 850.degree. C., with the partial pressure of oxygen in the exhaust gases.
Exhaust gas sensors of the type to which the improvement of the present invention is directed have been fabricated using a titania oxygen sensing element of discshape. The titania element has electrode wires embedded in it for conveying to an electronic control system an electrical signal resulting from variation in the electrical resistance of the titania disc. This variation occurs as the composition of the exhaust gases from an internal combustion engine is varied. The sensor electrical lead wires and the sensor itself are supported by a ceramic insulator mounted within a steel body that is attached to the exhaust conduit from the engine. As the sensor is subjected to exhaust gases of varying compositions, the varying electrical signal generated by the sensor passes through the lead wires in the ceramic insulator to terminal pins at one end of the insulator.
In the prior art exhaust gas oxygen sensor designs, such as those illustrated in the commonly assigned patent and patent application referenced above, the terminal pins have been held in place with a cement material which would seep out of a space between the terminal pins and the ceramic insulator. Also, the terminal pins would become loose after being subjected repeatedly to the temperature variations and conditions that occur in the use of an exhaust gas sensor in a motor vehicle. In this regard, it may be appreciated that an exhaust gas sensor, including its ceramic insulator and terminal pins, is repeatedly heated to high temperatures and then cooled to atmospheric conditions during ordinary use of a motor vehicle in which the sensor may be installed. The exhaust system of an internal combustion engine itself is a severe environment and that, coupled with the temperature cycling just mentioned, has tended to result in weakening and failure of the bond formed between the terminal pins and the ceramic insulators.